1. Field of the Invention
The present invention relates in general to a lock device for an automotive steering column and more particularly to a lock device for an automotive tilt-type steering column. More specifically, the present invention is concerned with a tilt-lock device by which the tilt-type steering column can be tightly and adjustably fixed to the vehicle body at a desired angle.
2. Description of the Prior Art
Hitherto, various lock devices for tilt-type steering columns have been proposed and put into practical use in the field of wheeled motor vehicles. With such lock devices, the tilt-type steering column can be fixed to the vehicle body at a desired angle to allow a driver to have an ideal driving posture.
In order to clarify the task of the present invention, one known lock device for the tilt-type steering column will be briefly described with reference to FIGS. 7 and 8 of the accompanying drawings, which is shown in Japanese Patent First Provisional Publication 6-286621. For ease of description, such lock device will be referred to as "tilt-lock device" in the following.
The tilt-type steering column shown in FIGS. 7 and 8 is of a lower-pivot type which has a lower portion pivotally connected to a lower part of a vehicle body and an upper portion detachably and adjustably fixed to the vehicle body through the tilt-lock device.
That is, as is seen from these drawings, the tilt-lock device comprises an upper clamp 3 which is secured to a robust structure of the vehicle body under a dashboard or the like. The upper clamp 3 is formed with two side walls 3a and 3b between which a generally rectangular recess 3c is defined. The rectangular recess 3c extends generally vertically. The side walls 3a and 3b are spaced from each other by the distance "A". Vertically slidably held by the upper clamp 3 is a distance bracket 5 which has side walls 5a and 5b intimately slidably engaged with inside surfaces of the side walls 3a and 3b of the upper clamp 3. For this sliding connection, the distance "B" between the side walls 5a and 5b of the distance bracket 5 is determined substantially the same as the distance "A". The side walls 5a and 5b are formed with inwardly bent support portions 5a' and 5b' for supporting and holding a jacket tube 2 of the steering column. As is seen from FIG. 8, the side walls 3a and 3b of the upper clamp 3 are formed with aligned elongate openings 6a and 6b (only 6a is shown) each extending vertically, while, as is seen from FIGS. 7 and 8, the side walls 5a and 5b of the distance bracket 5 are formed with aligned circular openings 7a and 7b is each having a diameter substantially equal to the width of the elongate openings 6a and 6b.
As is seen from FIG. 8, a tightening bolt 8 passes through the elongate and circular openings 6a, 6b, 7a and 7b which are aligned. Although not shown in the drawing, a nut is secured to the left side wall 3a (when viewed in the drawing) of the upper clamp 3, with which a threaded left end of the tightening bolt 8 is operatively engaged. Thus, when the tightening bolt 8 is turned about its axis in a fastening direction, the side walls 3a and 3b of the upper clamp 3 are forced to bend toward each other thereby to grip the distance bracket 5 therebetween tightly. With this, the jacket tube 2 of the steering column is tightly held by the tilt-lock device. While, when the tightening bolt 8 is turned in an unfastening direction, the tight engagement between the distance bracket 5 and the upper bracket 3 becomes cancelled. Under this condition, the distance bracket 5 can be easily moved or pivoted up or down together with the jacket tube 2 by a degree determined by the length of the elongate openings 6a and 6b. That is, the steering column can be shifted or pivoted to a new angular position. Thereafter, the tightening bolt 8 is turned in the fastening direction. With this, the steering column is fastened to the vehicle body at the new angular position.
However, due to its inherent construction, the above-mentioned known tilt-lock device has the following drawbacks.
That is, as is seen from FIG. 8, when the tightening bolt 8 is turned in the fastening direction, the side walls 3a and 3b of the upper clamp 3 are forced to incline toward each other. However, such inclination of the side walls 3a and 3b tends to produce a wedge shaped gap "S" between each side wall 3a or 3b of the upper clamp 3 and the associated side wall 5a or 5b of the distance bracket 5. As is seen from the drawing, production of such gap "S" causes insufficient coupling between the upper clamp 3 and the distance bracket 5. In other words, as shown in the drawing, due to production of such gap "S", the practical distance "H" between the upper clamp 3 and the distance bracket 5 becomes large because actually these two parts are connected to each other at their mutually contacting portions which are pressed against each other by the tightening bolt 8, which induces a poor grasping of the jacket tube 2. In fact, such insufficient coupling brings about a higher possibility of transmitting undesired engine vibration to a steering wheel (not shown) mounted on the steering column, which gives the driver an unpleasant feeling. Furthermore, such insufficient coupling tends to produce noises particularly when the tilt-lock device is used for a long time.